An inverter is a device configured to control a motor speed and a motor torque. Although there are several methods for motor speed control, representative methods include a primary voltage control method and a frequency modulation method. An inverter may be used for efficiency control and power factor control, and may be applied to and used for spare power source, non-interrupting electric source and linear transmission.
The purpose of inverter is to perform a process control, factory automation and energy saving. For example, an inverter in a blower may adjust speed of the blower in response to types of product and output of the product. The adjustment of wind amount by a blower can adjust a temperature inside the blower to an optimum temperature, and promote improvement of product quality as well, whereby a great energy saving effect can be brought. Currently, researches on technologies for efficiently controlling an inverter are being briskly waged, in case an instantaneous interruption occurs.
Conventionally, a design must be made in a manner such that an inverter is mounted with a noise prevention part on a power input unit in order to operate without erroneous operation caused by harmonic noise introduced from the power input unit or internal switching noise, or the ground of a control circuit, an analogue circuit and power supply circuit is electrically isolated to interrupt noise introduced from the power supply circuit to the control circuit or the analogue circuit.
However, it is difficult to mount a noise prevention part to a power input unit, or to electrically isolate the ground of a control circuit, an analogue circuit and power supply circuit due to limit in product size, in case of a small-sized inverter product. An inverter that is not electrically isolated in the ground of power supply circuit has a structure susceptive to harmonic noise. A small-sized inverter cannot alleviate the harmonic noise introduced into an input unit due to difficulty in mounting a varistor on a 3-phase power input unit due to problem of product size.
Although resistance to harmonic noise may be increased by designing a noise reduction filter on an inverter protection circuit, a sensing circuit and a connection unit of a control circuit, there is a limit due to generation of loss or delay of control information.